A vinyl chloride-based polymer is a resin containing 50% or more of vinyl chloride, wherein it has various applications because it is inexpensive, its hardness is easily controlled, and it is applicable to most processing equipments. In addition, since the vinyl chloride-based polymer may provide a molded article having excellent physical and chemical properties such as mechanical strength, weather resistance, and chemical resistance, the vinyl chloride-based polymer is being widely used in many fields.
The vinyl chloride-based polymer is prepared in different forms depending on the application. For example, a vinyl chloride-based polymer for straight processing, such as an extrusion process, a calendaring process, and an injection process, is generally prepared by suspension polymerization, and a vinyl chloride-based polymer for paste processing, such as dipping, spraying, and coating, is prepared by emulsion polymerization.
In the paste processing, a vinyl chloride-based polymer latex for paste processing obtained by emulsion polymerization is generally dried by a spray drying method to form final resin particles, and the particles are dispersed in a solvent or a plasticizer and used in products, such as a flooring material, wallpaper, a tarpaulin, a raincoat, gloves, an automotive underbody coating, a sealant, and carpet tiles, through a process such as reverse roll-coating, knife coating, screen coating, spray coating, gravure and screen printing, rotation casting, and shell casting and dipping.
The vinyl chloride-based polymer for paste processing is difficult to be applied alone due to low processability and is normally processed and used in the form of a plastisol which is composed of various additives, such as a heat stabilizer, as well as a plasticizer, and, in this case, in order to obtain excellent processability, it is important to maintain good flowability by reducing viscosity of the plastisol.
In particular, with respect to a vinyl chloride-based polymer used in a sealant or an automotive underbody coating, the vinyl chloride-based polymer is coated on an adherend by spray coating and then subjected to a drying process, wherein, in a case in which viscosity of the vinyl chloride-based polymer is low, the vinyl chloride-based polymer is formed into droplets or is detached from the adherend while having fluidity due to gravity before drying. As a result, since a coating thickness becomes non-uniform and the vinyl chloride-based polymer is thinly formed at a specific site, failure may occur.
Also, in order to use the vinyl chloride-based polymer in a coating process using spray coating, flow characteristics of a pseudoplastic fluid, in which viscosity and stress are reduced as shear rate increases, must be achieved.
Thus, in order to use the vinyl chloride-based polymer in a sealant or an automotive underbody coating through a coating process using paste processing, for example, spray coating, there is a need to develop a vinyl chloride-based polymer which may exhibit high viscosity characteristics in a region of low shear rate or zero shear rate and may have characteristics in which viscosity and stress are reduced as the shear rate increases.